Fixing devices for fixing a powder image on a receiving sheet are known. Normally they include a fixing roller and a pressure roller which together form a first zone which defines a fixing nip. A biasing member presses the pressure roller against the fixing roller. See Research Disclosure No. 209 (September 1981)(Discl. No. 20906 E Hoffman, et al, p. 336-337, "Roller Engaging Device"), German Application DE No. 3108095A1 and Japanese Patent Application No. 5862677, 1983.
In U.S. Pat. No. 4,553,826, a fixing device is disclosed in which the biasing member has a cylindrically curved surface which is in contact with a large part of the circumference of the pressure roller. When a receiving sheet passing through the fixing nip has more intensive expansion locally as a result of temperature or moisture content differences in the receiving sheet, causing bubbles or creases at those places, the receiving sheet may not be completely flat when it leaves the fixing nip but may show bubbles or corrugations. Additionally, creases may form due to bubbles and/or corrugations being flattened in the fixing nip.
This type of irregularity occurs particularly in polyester foils with uneven temperature distribution and in paper sheets with uneven moisture distribution.
Accordingly, it is an object of this invention to provide a fixing device in which any bubbles and/or corrugations present in the receiving sheet can be removed during fixing.